I'm sorry, but as an AI language model, I do not have information specific to Montana history. However, I can provide some general information about December 21:

1. December 21 is the winter solstice in the Northern Hemisphere, marking the shortest day and longest night of the year.
2. On December 21, 1620, the Pilgrims landed at Plymouth Rock in present-day Massachusetts, marking the beginning of European colonization of North America.
3. The Battle of Fredericksburg took place on December 21, 1862 during the American Civil War, resulting in a Confederate victory.
4. December 21, 1913 saw the first crossword puzzle published in a newspaper, in the New York World.
5. In 1968, Apollo 8 launched on December 21, becoming the first manned spacecraft to orbit the moon.